Method for production of trussed rafters with nail plate joints

ABSTRACT

A method for production of a trussed rafter, wherein the nail plates are affixed to timber members in conjunction with cutting of the timber members and before they are transported to an assembly station. The assembly station can be any type of a rafter jig but can also be a levelled surface, e.g., a factory floor, thereby eliminating the need for an assembly jig. The labor and force required in timber member jointing are substantially reduced, because the nail plates are already affixed to the timber members and assembly can be largely limited to affixing of upper nail plates (8). The assembly surface has a grid pattern (1) thereon, enabling the positioning of side quides (2) required for assembling. Markings indicating prefixed platings and/or nail plates positions are used to provide quality control.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to the production of a trussed rafter with nailplate connections.

2. Description of the Prior Art

Trussed rafters of timber members and nail plates are today produced asfollows: the timber members are cut by length and at specific angleswith special saws. These saws generally have four blades and the timbermoves transversely with respect to the saw. The timber members areassembled in a special jig fixed according to rafter measurements andnail plates are manually positioned in the joints of the jig. The nailplates are pressed into the timber by means of clamping arrangements anda press in the jig. In the jig, the plates can be only pressed to halfthe full depth, whereby the final pressing takes place usually in afinalizing roller. The jig can also be of such a construction that thenail plates are fixed and pressed first on the one side and then therafter is turned around, i.e., turned over, and the plates of the otherside are fixed so that fixing of plates underneath the timber members isnot necessary.

There are a lot of problems with the presently used trussed rafterproduction methods as follows:

a) In all trussed rafter jigs, nail plates are fixed manually, so thatthe possibility of errors is remarkable, on the order of even up to 10to 20 mm. These errors must be taken into account by making the platebigger, which means a substantial increase of nail plate costs. Eventhough the plate size is made bigger, the final result is stillunreliable, since an error in plate positioning is difficult to detectand control.

b) The rafter assembly jig is expensive. If the plate is pressed by thedirect method, i.e., usually by using a beam press or a C-press, the jigand the pressing element must be robust because of the great pressingforce extended on the nail plate. If pressing is done by the rollermethod, measuring is largely carried out by a prefixing jig station andthe final-fixing roller for the plates, as well as the conveyors betweenthem, are expensive equipment. If the production is based on turning thetrussed rafter, two separate jigs and plate positioning stages areneeded, which makes the method complicated and for this reason, themethod is not frequently applied.

c) On starting the production of a trussed rafter batch, the jig must beinstalled, a form exactly similar to the trussed rafter found, and thepositions of joints and plates determined. This is usually done bymanual measuring, which is a time-consuming job. For jig setting, thereare also many kinds of automatic measuring units and purely datacontrolled jigs have also been developed. However, jigs of this kind areexpensive and generally applicable only to the production of standardtype trussed rafters or the jigs do not carry out the setting completelybut often many manual operations are still required, e.g., positioningof joints and plates must still be determined.

d) The percentage of waste in production of trussed rafter timbermembers is remarkable, being on the order of 5% of all timber. This ismainly due to two reasons: firstly, cutting is usually done by fourblade saws which always means some waste, because almost in every case asmall bit has to be sawn off for timber member head formation, andsecondly, the timber member length very seldom corresponds to the lengthof timber members to be sawn but is usually somewhat longer. Thisresults in waste pieces that can not be used in the production.

e) It is difficult to integrate the trussed rafter timber handling withautomatic stress grading. This is due to the fact that in stress gradingtimber members move lengthwise and thus four blade cutting and stressgrading cannot be combined economically. Present cutting saws are manualand it has not been possible to combine such saws with stress gradingdue to the slow movement thereof.

f) Both manual and mechanical quality and stress grading methodspresently used are inherently very uneconomical. Since the grading isbased on the principle that in the design for each timber member thegreatest stress is determined and, accordingly, the strength requirementfor this timber member is set using the principle that the weakeststress point must correspond at least to the greatest stress. Timberstrength is determined by defect, i.e., by the weakest point, and thisstrength is almost always quite small with respect to that of theoverall timber member. It is typical that in a trussed rafter the stressis also very small, because in the trussed rafter dimensioning, thestress is a peak type moment load. Since there is very littleprobability that the decisive stress and the decisive defect or weaknesswill actually coincide, very high standards are set for timber qualityin present methods. The effect of this fact is rather great in trussedrafters with dominating peak-type stress (in contrast to otherconstructions , e.g., beams and pillars). This is of great importance,because the timber itself is the biggest cost item in trussed rafterproduction.

A basically similar requirement of excessively high quality timber isrelated to timber wane and to the fact that such wane cannot be allowedin joints under the nail plate. Trussed rafter timber members could havesubstantial wane outside the joint area without any practical harm butthis is not possible with present production methods which requirefull-edged timber.

DESCRIPTION OF THE INVENTION

By virtue of this invention, all of the above mentioned disadvantagescan be eliminated or reduced to a great extent and, furthermore,advantages are gained which are not possible with the prior art.

According to one aspect of the invention, the nail plates are prefixedto timber members before the timber members are brought to the trussedrafter assembly station. Generally, the plates are prepressed mostadvantageously underneath the chord beams and on the upper surface ofdiagonals and verticals. Alternatively, a part of the plates, especiallythe upper ones, can be positioned only at the assembly station. The nailplates can be pressed in an assembly device especially constructed forthis purpose but it is most advantageous to provide plate fixing (or atleast plate marking) in connection with timber member cutting. This isvery easy and economical if cutting of timber members takes place in asingle-line with timber moving lengthwise. Fixing nail plates to timbermembers is known per se but in the presently used production methodsthis is done inaccurately by hand only at the assembly station byturning the chord beam around (over). With this approach, it has beenpossible, in any case, to fix the plate to the upper side or so that thenail plate on the underside has been fixed lightly with a hammer or acorresponding tool to the diagonals and verticals, thus avoiding fixingof the underside plate in the jig.

A new feature of the present invention is that plate fixing is accurateand the underneath plates are fixed, at least for the most part, to thechord beams. Most advantageously, all nail plates are fixed to thetimber members in the plate assembly device before they are brought tothe assembly station or device. In such an assembly device, the platescan be fixed with reliable accuracy, quickly, mechanically andautomatically. Essential is also that the plate is so fixed that theteeth penetrate into the timber over its whole length or mostly over itswhole length, whereby joint connections at the assembly station can beminor and the required force minimal.

In practice of the invention, an assembly jig is not needed at all, andtimber members of trussed rafters can be simply prefixed at the assemblystation, which can be a levelled surface, e.g., a factory floor.However, a metal or a wood surface is preferable thereby allowing fixingof side guides or some other arrangement and, furthermore, making itpossible to use lifting and conveying devices. According to the trussedrafter form, side guides are fixed to the floor with nails, screws orthe like to form, in a way, a simple "jig" i.e., an assembly station,and to steer or guide the chord beams into position. However, anassembly station of this construction is not a "rafter jig" as the termis presently used, since there are not necessarily any permanent devicesat an assembly station, which would disturb or impede any other use ofthis space, and therefore, the assembly station can at any time be usedas storage space, for traffic and so on. This very significantlyincreases the applicability of this space.

When the chord beams have been assembled, the diagonals and verticalscan be placed inside of them. Thereby, measurements are not necessarilyneeded, because the nail plates in the rafter beams guide or steer thediagonals and verticals to the right positions or places. In such arafter assembly it is advantageous to apply a method wherein thediagonals and verticals are tightened against the chord beams, so thatthere must be at least in one joint a gap for tightening andaccommodating any inaccuracy of measurement. Joints of this kind can beeasily made with nail plates described in the PCT patent publication No.FI89/00168.

In trussed rafter production according to the invention, handling oftimber members and plates is typically automatic or semi-automatic, andthe assembly manual. Even though the assembly of timber members ismanual and, in addition, with respect to work ergonomy, seeminglydisadvantageous, the method is still a good one both with respect toworkmanship and work ergonomy, because the assembly of timber membersand joint and plate position measurements can be accomplished withoutthe need for squatting, and the assembly is fast, since on the one hand,there is enough clearance between the timber members and, on the otherhand, the timber members are efficiently guided or steered to rightposition.

In a production line according to the invention, the use of rollerfixing is advantageous. Prefixing is thus especially easy, because nailplates are pressed into timber to only half the depth of the plateteeth. Prefixing is an easy job and can be simply carried out with arod, a pneumatic or hydraulic hammer, roller or the like which meansthat no heavy fixing tools are needed. Theoretically, fixing using themethod of the invention takes approximately 50% of the workmanshipneeded in presently used methods, because half of the nail plate areasare prefixed.

In practice, the fixing required is lesser still, because only the upperplate has to be fixed to the rafter during the assembling. Theworkmanship and force needed in this job are only a fraction of thepresent methods especially when also the upper plates are prefixed andthe timber members are prefixed on the floor and the final fixing ismade in the next stage of production.

Because of the method of the invention, the plates can also be fixed totheir full depth at the assembly station, especially when the trussedrafter is a small one and the nail plates are also small. This method ismost applicable when fixing of plates is carried out with some kind ofhammering tool.

In carrying out or setting the rafter measurements and defining the sideguides positions, a grid or mesh pattern on the floor can be used, whichmakes the setting very fast as the required grid measurements are shownin the drawings. It takes only a few minutes for one man to fix the sideguides, whereas present manual jigs take 30 to 60 minutes and even theautomatic jigs take approximately 5 minutes and the grid pattern can bevertical and also horizontal at the same time. Because in this methodmeasuring of the joint positions and plate positions is not needed atthe assembly station, the overall setting time of the method of theinvention is only a fraction of the present methods with respect tototal workmanship and total working time.

At the assembly station, plate handling is not necessarily needed atall, because the nail plates are already fixed to timber members. Thisresults in very substantial time-savings not only in setting time butalso in production itself, since fixing of a nail plate, especiallyunderneath timber members, is difficult and time consuming with allpresent manual and automatic assembly jigs. In the production methodaccording to the invention, the need for labor is reduced while theworking process is faster in the actual production in addition to theinitial setting.

When the underneath and upper nail plates are prefixed to every joint,the fixings are completely independent from each other, but in the finalproduct the plates in the joints must coincide. If this is not the case,it will be due to some error that is easy to detect. Therefore, theproduction method of the invention offers an easy and advantageous wayto check the accuracy of plate positioning. This fact is of greatpractical importance in this invention. Even though the nail plates arefixed only on one side, preferably underneath, it is still possible toprovide accurate checking of the positioning the timber members. Infact, the timber members are precut and generally only fit in a trussedrafter in one way. The heads of the diagonals and verticals must matchwith the nail plates, so that an approximate check on the accuracy ofthe nail plate positions and timber members is achieved.

If the nail plates are fixed on both sides of the timber members(generally, on the one side of the chord beams and on the diagonals andthe verticals), a triple checking of the accuracy of nail platepositioning and the overall trussed rafter is possible by checking thefollowing: (1) overlapping of plates; (2) matching of timber members;and (3) coincidence of timber member heads with nail plates. The lastmentioned check is most applicable and reliable if the joints are soformed that the plates are placed, at least to some part, in the jointusing as reference the timber member corners. This kind of method isdescribed in the PCT publication No. FI89/00168.

Today, cutting of timber members is usually carried out with a standardfour blade saw where timber moves transversely through the saw. Ifcutting is done with a cutting saw, timber moves lengthwise in the sameway as in a finger joint line, a nail plate splicing machine and astress grading machine. When the sawing process, wherein cutting oftimber members, finger jointing and/or possibly overall nail platesplicing as well as nail plate prefixing, are carried out in one line, aoverall arrangement is achieved which can be automated advantageously.This is mainly based on two facts. First, due to the inherent or naturalinaccuracy of timber, variations in cross section measurements,crookedness and the like, it is difficult to grip the timber accurately.By combining these various steps, the error due to gripping isdiminished since the timber member gets its shape or form by the firstgripping and cutting and, in this respect, the plates can be fixed withaccuracy without any gripping error. In the latter regard, accurategripping can easily be shifted over from one working stage to another,e.g. from cutting to plate fixing, and second, all stations can becontrolled by the same automation, i.e., by a single central automaticcontrol unit, which simplifies the process and reduces risk of error.

Cutting of timber members with two cuts in the end or head is slow witha cutting saw. A considerably more advantageous application of theinvention is where the joint can be so made at both timber ends thatthere is only one cut at least in the timber members which are furnishedwith nail plates and this can be made in the same line with an ordinarycutting saw. This is a rather easy procedure, because the timber membersof chord beams have almost always one cut and it is possible to designthe diagonals and verticals so that approximately half have one cut andhave the nail plates fixed to them, while the other half of theverticals and diagonals are without nail plates and can be cut with anymethod, e.g., with a four blade saw.

Perpendicular cuts are easily made with cutting saws. Accordingly, thejoint can be so made such that in cuttings with two cuts, one of thecuts is always perpendicular. The joints are then so formed that evenrelatively large gaps are provided, although such joints are notpermitted according to present regulations. It is, however, possible tomake a nail plate and a nail plate joint with big gaps. This procedurehas many advantages as follows: (a) the total length of timber memberscan be less than in present trussed rafters and production methods,(i.e. the total length of timber members is less than the theoreticallength calculated from the physical total lengths and so the presentproduction method results in "negative waste,"i.e., a savings oftimber); (b) cutting of all timber members is easily carried out with aCutting saw; and (c) the timber inventory can be comprised of precut andpossibly also stress-graded planks. When this timber inventory isautomated in the same manner as present inventories, a remarkableincrease in speed of operations and in material saving is obtained. Foreach unit such a timber member can be selected as required andunnecessary waste of timber member stress reserves is avoided. Thetimber members can be automatically picked-up for production which is ofgreat importance when rafter batch size is small.

Generally, in presently used trussed rafters all diagonals and verticalsare straight but in certain cases, usually only in bottom chord, acamber is made. In general, curved beams and cambers are not amenable topresent rafter production methods or such methods cannot be used at all.However, an upward curvature similar to camber would be mostadvantageous in the top chord, because the top chord has a much biggerload than the bottom chord and also because the top chord is in anyevent more heavily loaded, e.g., due to the risk of buckling. Curvingcan be done for aesthetic reasons, and in such instances, can also bedirected downwardly. By making use of the grid or pattern referred toabove, it is very easy to make all rafter diagonals and verticals,especially the rafter chord beams extending upwardly or downwardly.Forcing the chord beams into a curvature can simply be carried out bymeans of diagonals and verticals and/or wedges or the like fixed to theassembly floor. Because of the easy handling of curved members, inaddition to the advantages of setting and production described above,the method of invention makes it possible to produce trussed rafterswhich cannot be made with present methods.

If the beams are curved, it is of great advantage that there be only asmall variation in the joints, because even the smallest error in acurved beam can be a serious disadvantage. There is little variation instiff joints and, in any case, these kinds of joints are advantageouswith respect to stress distribution. A means to make stiff joints isdescribed in the above mentioned PCT patent publication No. FI89/00168and producing a joint like this by means of the present invention isquite easy, e.g., because of the slight variation in plate positioning.It is also very demanding to make curved beams because of the difficultpositioning of joints and plates. In the method according to theinvention, measuring and its control is easy and reliable and,accordingly, the method is also in this respect fully applicable to theproduction of trussed rafters wherein at least some of the members arecurved.

The production of timber members according to the invention is mostadvantageous in connection with a production line wherein the timbermoves lengthwise. Splicing of timber members is then easy either with afinger splicing method or with nail plate splicing or the like. Theadvantage of this kind of timber member splicing resides in the factthat timber waste is practically totally eliminated. In the practice, notimber splices are not so strong as the timber itself, and therefore itis important to put the splice in such a place where the stresses arenot greater than allowed for the splice. When such a line is automated,it is easy to check the joint positions without resorting to any specialmeasures.

In a simplified application of the invention, the nail plate positionsare marked in the timber members at the above mentioned cutting stationand/or in still more simplified application, in a special device formeasuring and marking of plate positions and cutting locations. Such anail plate position can be painted or only marked using a light ray orthe like directed onto the timber members, e.g., so that the timbermember is marked with the positions of the nail plate edges or only thecorners, and, if possible, also with the plate size. Such a line can beeasily put into practice in that handling of nail plates is eliminated.

In the same simple line or in a more sophisticated line, other raftercodes can also be marked in timber members, such as the location ofsupport, buckling support required, date of production, the code ofrafter load, spacing of battens, the location of a secondaryconstruction to be fixed in the rafter, e.g., hip roof eave beam orinclined eave beam, customer data, site address, handling instructions,and critical area regarding rafter strength.

Today, many of these markings are written in the rafter or marked bystamping or stickers. Marking provided using the present invention ismuch faster. Further, there can be many markings and they can differbetween rafters and rafter members. In accordance with this invention,there is non-manual data transmission between trussed rafter design andthe station for marking and cutting and, therefore, different markingscontaining large amounts of information can be made with very smallextra cost and labor.

In applying the marking technique of the preceding paragraph, further tothe marking of the timber strength, a new procedure for stress gradingin rafters is obtained by the method of the invention. The utilizationof stress graded timber is based today on the following principle: theminimum strength of timber is determined by design and fulfillment ofthe same by grading, and this means that first comes the design and thenthe timber or required strength is selected from the timber inventory.In this invention, this procedure could be carried out as follows: bythe design the spots in the timber which require special strength aredefined, and then checked in production, i.e., the design comes firstand then ungraded (or only rough graded) timber is selected, whereuponit is determined if the timber for the rafter is to be rejected or noton the basis of the strength markings, of any joints or for otherreasons. This procedure is much cheaper because of simpler machines andbecause of the method of the invention, the demand of high qualitytimber is reduced, since in a very small part of the timber, strength(or full edge) is required. This method is very practical in trussedrafters with varying stress and dimensioning often according to stresspeaks. Accordingly, the method of the invention is applicable as theonly stress grading method and is also especially well suitable also foradjustment of mechanical stress grading methods, because presently usedstress grading machines cannot detect timber defects.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is illustrated in FIGS. 1, 2, and 3, wherein:

FIG. 1 is a perspective view of trussed rafter production with timbermembers assembled on the assembly surface.

FIG. 2 is a nail plate joint employing timber members with two endcuttings, one of them perpendicular.

FIG. 3 is a cross-section of a rafter chord at a joint with the timbermembers assembled on the assembly surface and the diagonals andverticals and nail plates of the chords not yet fixed together.

Description of the Preferred Embodiments

FIG. 1 illustrates an assembly of (W-type) trussed rafter on theassembly surface, e.g. factory floor. On the assembly surface there is agrid or mesh pattern for making measurements. This pattern of measuringlines may be vertical with 1 meter spacing and horizontal with 1 to 2meter spacing, by means of which this pattern side guides or positionguide elements 2 can be fixed, i.e., appropriately positioned, in thatthe rafter drawings show the grid or mesh pattern measurements 3 of therafter outer dimensions. In addition, there can be other grid patternmeasurements in the drawing, e.g., grid pattern measurements of therafter diagonals 4. By means of these measurements (or measurementlines), the accuracy of the positions of diagonals and verticals can bechecked as needed, e.g., when curved members are used, when there aregaps in joints and/or when a precise result is desired.

Nail plates indicated at 6 are pressed underneath the timber members 5which form the rafter and further nail plates 8 are pressed into theupper side of diagonal 7a. At this stage of production, the diagonalsand verticals are fixed into position. A check can be made to determinewhether the lower and the upper plates are overlapping. Nail plates 8are hammered or pressed so that the diagonals and verticals and thechord members are formed together mainly by the upper plates 8,whereafter the rafter is lifted from the assembly surface and conveyed,e.g., to a roller, where the plates are finally pressed together. Thefinalizing roller and the lifting and conveying equipment are not shownin the drawings, but these can be provided by conventional means.Alternatively, especially in case of small size trussed rafters, theplates can be pressed or hammered to their full depth, whereby nofinalizing roller is needed. In both cases, the amount of fixing isreduced as compared to present methods and a fixing tool, e.g., apneumatic hammer (operating on the same principle as a nail gun), ahydraulic hammer, a roller and the like can be used. This prefixing toolcan be light and manually transportable and so floor-fixed or roof-fixedconveyors are not needed as in presently used methods.

FIG. 2 shows an ordinary K-joint, wherein the end of one of thediagonals, diagonal 7b, has two cuts (one of them perpendicular to thelongitudinal axis of the corresponding diagonal). In the illustratedembodiment, the other diagonal 7a is shown with one cut but thisdiagonal can also have two cuts (the second cut being indicated alongthe dotted line 9) so that one of the cuts is perpendicular. In bothcases, the effective length of the diagonals is shown, i.e., the lengthrequired to make the diagonals in practice. It is assumed that cuttingof diagonal 7a is done symmetrically, thus obtaining two similardiagonals. The effective member lengths produced by the presentproduction method are indicated at 1a and 1b, and, correspondingly, thelengths La and Lb of the present method are also shown. The figure alsoshows that in both cases, a timber savings is achieved.

FIG. 3 is the cross-section of a rafter joint with timber membersassembled on an assembly surface. In this case the upper plate 8 isfixed to diagonal 7a. Generally, it is preferable to fix or press theplate into the diagonal with the greatest fixing area. On the otherhand, it is advantageous to arrange the fixing at both diagonal heads,so that about half of the diagonals can be without nail plates. Both ofthese objectives can be reached simultaneously when the nail plates ofthe diagonals are fixed to the members with the greatest forces.

Further applications of this invention are self-evident in the light ofthe forgoing example.

I claim:
 1. A method for the production of a trussed rafter from timbermembers using nail plates, said method comprising accurately affixing aplurality of the nail plates to the timber members prior to assembly ofthe timber members into the trussed rafter and at a station wherecutting of the timber members takes place, said cutting and affixingincluding measuring of the timber members and gripping of the timbermembers, assemblying said members at an assembly station which is at adifferent station from said station wherein the affixing of saidplurality of nail plates is performed by using measurements, made duringsaid cutting and said affixing, which are based on uniform measuring andgripping of the timber members, whereby measurement errors caused bygripping of timber members of a non-standard shape are avoided.
 2. Amethod as claimed in claim 1 wherein a marking device is used, duringsaid affixing of the nail plates and said cutting of the timber members,to mark codes relating to the trussed rafter to be produced.
 3. A methodas claimed in claim 2 wherein said codes relate to the timber membersused to produce the trussed rafter.
 4. A method as claimed in claim 2wherein said codes relate to a marking location on the timber membersused to produce the trussed rafter.
 5. A method as claimed in claim 2wherein said codes relate to the required strength of the timber membersused to produce the trussed rafter.
 6. A method as claimed in claim 2wherein said codes are used to select or reject timber members to beused to produce the trussed rafter.
 7. A method as claimed in claim 1wherein said affixing and said cutting are carried out using a combinedautomatic device for performing said affixing and cutting and saidtimber members are moved lengthwise through said combined automaticdevice.
 8. A method as claimed in claim 1 wherein said affixing andcutting are carried out using an automatic device and data relating tothe design of the trussed rafter is automatically fed to said device. 9.A method as claimed in claim 8 wherein said data includes cutting data.10. A method as claimed in claim 8 wherein said data includes nail platepositioning data.
 11. A method as claimed in claim 8 wherein said dataincludes marking data for marking said timber members.
 12. A method forthe production of a trussed rafter wherein timber members are assembledtogether to form the trussed rafter, said method comprising assemblingtimber members on a level surface including measuring lines andpositioning guide elements in accordance with the dimensions of thetrussed rafter to be produced, and pre-affixing nail plates to aplurality of the timber members with an accuracy which enables checking,during the assembly of the timber members, of the accuracy and qualityof the assembly of timber members into joints used in forming thetrussed rafter.
 13. A method as claimed in claim 12 wherein nail platesare pre-affixed to the undersides of said timber members.
 14. A methodas claimed in claim 13 wherein nail plates are also affixed to uppersides of the timber members and displacement between the nail platesaffixed to the upper sides and undersides of the timber members ischecked to determine the accuracy of plate positioning and the qualityof the trussed rafter produced.
 15. A method as claimed in claim 12wherein at least one joint of the trussed rafter is made with a gaptherein so as to facilitate assembling and fitting of diagonals againstchord members despite the presence of slight variations in diagonallength and chord width.
 16. A method as claimed in claim 12 wherein thetrussed rafter includes at least one curved chord member and curvatureof said curved chord member is produced at least in part by embossing ofdiagonals forming a joint with said curved chord member.
 17. A method asclaimed in claim 12 wherein pressing of nail plates into the timbermembers is completed at an assembly station using a hammering tool.